The present invention relates generally to cathodic arc coating and, more particularly, to an improved cathode mounting system for cathodic arc cathodes.
The cathodic arc process is known in the art as a robust, relatively inexpensive technique for deposition of single and multi-component metallic and nonmetallic coatings. Cathodic arc deposition systems consist of a vacuum chamber which includes an anode, a power supply and a cathode. The cathode material is deposited during the operation of the system.
Often, these cathodes are mounted to the electrical (and cooling) source by means of a threaded stud. The stud is screwed into the back of the target and the stud/target assembly is then screwed to the electrical and cooling block. In certain instances, the materials to be used for deposition are difficult to manufacture with threaded mounting holes. Not only may an expensive sample be damaged but also the cost to machine each sample can become prohibitive.
Thus, there remains a need for an improved cathodic arc coating apparatus able to mount cathodes with much less machining while, at the same time, providing sufficient strength to hold the cathode in place.
The present invention is directed to an apparatus for cathodic arc coating. The apparatus includes: a vacuum chamber which includes an anode; a power supply; and a cathode target assembly connected to the power supply. The cathode target has an interference fit stud with a threadless distal end. In the preferred embodiment, the distal end of the threadless cathode target also- includes a predetermined surface texture and a cooling block in contact with the cathode target.
The cooling block includes a chamber adjacent to the cathode and a cooling fluid supply contained within the chamber. A fluid seal between the cooling block and the cathode prevents leakage of coolant into the vacuum chamber. The cooling fluid supply includes an inlet for providing cooling fluid into the chamber and an exit for withdrawing the fluid from the chamber.
The vacuum chamber includes an enclosed chamber and a staged pump for producing a vacuum therein. In the preferred embodiment, the power supply is a continuous DC power supply of greater than about 60 amps at about 20 volts.
In the preferred embodiment, the surface of the distal end of the stud is either smoothed for use with targets formed from materials harder than the materials used to form the stud, or textured for use with targets formed from materials softer than the materials used to form the stud.
In one embodiment, the interference fit is a thermally formed interference fit, wherein the material of the stud is pre-selected to have a thermal expansion coefficient greater than the thermal expansion coefficient of the material of the target, thereby maintaining the interference fit as the target is heated during use.
In another embodiment, the interference fit is a mechanically formed interference fit, wherein the mechanically formed interference fit includes a cylindrical opening in the distal end of the stud, a wedge adapted to be received within the cylindrical opening, and a screw extending through the stud into the wedge, whereby tightening the screw expands the outer walls of the cylinder of the stud to form the interference fit.
Accordingly, one aspect of the present invention is to provide an apparatus for cathodic arc coating. The apparatus includes: a vacuum chamber which includes: an anode; a power supply; and a cathode target assembly located within the vacuum chamber and connected to the power supply, the assembly having an interference fit stud with a threadless distal end.
Another aspect of the present invention is to provide a threadless cathode assembly for a cathodic arc coating apparatus. The threadless cathode assembly includes: a cathode target and an interference fit stud with a threadless distal end, wherein the distal end further includes a pre-determined surface texture.
Still another aspect of the present invention is to provide an apparatus for cathodic arc coating. The apparatus includes: a vacuum chamber which includes: an anode; a power supply; a cathode target assembly located within the vacuum chamber and connected to the power supply, the assembly having an interference fit stud with a threadless distal end, wherein the distal end further includes a predetermined surface texture; and a cooling block in contact with the cathode.
These and other aspects of the present invention will become apparent to those skilled in the art after a reading of the following description of the preferred embodiment when considered with the drawings.